1. Field of the Invention
The present invention relates to the field of dimerizing, co-dimerizing and oligomerizing olefins. More particularly, it concerns an improved catalyst composition for use in those reactions.
2. Description of the Prior Art
French Patent No. 2,611,700 describes the use of liquids with an ionic nature formed from aluminum halides and quaternary ammonium halides as solvents for organometallic nickel complexes for catalyzing olefin dimerization. The use of such media, which are not miscible with aliphatic hydrocarbons, in particular with olefin dimerization products, allows better use of homogeneous catalysts.
U.S. Pat. No. 5,104,840 describes a liquid composition with an ionic nature resulting from contacting quaternary ammonium halides and/or quaternary phosphonium halides with alkyl aluminum dihalides and an optional aluminum trihalide. That patent also describes the use of such media as solvents for transition metal complexes, in particular nickel complexes containing no nickel-carbon bond, which are transformed into catalysts for oligomerizing olefins. In the present text, these media will be termed “molten salts” as they are liquid at moderate temperatures.
That work shows that the most active and most stable nickel catalysts are obtained in “molten salts” constituted by one molar equivalent of ammonium halide and/or phosphonium halide with one equivalent and more of an aluminum trihalide, and optionally any quantity of an alkylaluminum dihalide. That formulation has been shown to be of particular advantage as the nickel complexes dissolved therein have a high catalytic activity.